An electrochemical cell has two electrodes, the anode and the cathode, separated by an electrolyte. An electrochemical cell can have a variety of functions, including as a battery cell, a capacitor cell, or a fuel cell. The electrochemical cell typically has two electrodes, an anode and a cathode, which are good electronic conductors and which store electric power as chemical energy in a battery cell and as surface electrostatic energy in a capacitor cell. Catalytic electrodes convert the chemical energy of a fuel to electric power in a fuel cell. The electrochemical cell also contains an electrolyte, which is located in series between the anode and the cathode.
Reaction between the two electrodes during charge or discharge of the electrochemical cell involves transfer of a positive charge between the two electrodes inside the electrochemical cell via the electrolyte. Negative charge is transferred during charge or discharge as electronic current in an external circuit. The electrolyte is an electronic insulator, so the negative charge is forced to be transferred via the external circuit; it cannot be transferred internally via the electrolyte.
In a traditional rechargeable electrochemical battery cell, both electrodes are sources and sinks of mobile cations (often referred to as the working ions) of the electrolyte. During charge one electrode acts as the source of the working ions and the other acts as a sink; these functions are reversed during discharge.
In a traditional electrochemical capacitor cell, electrostatic power is stored as electric power in two electric-double-layer-capacitors at the two electrode:electrolyte interfaces.